Computers are usually equipped to use a mouse for controlling the movement of the cursor. Computer mice employ mechanical, optical or other means to control the displacement of a cursor on a computer screen. By moving the mouse across a flat surface along two axes, the cursor is proportionally moved across the computer screen. Mouse usage is coming under increasing scrutiny because while providing the computer user with considerable flexibility over the motion of the cursor on the computer screen, extended or repeated use of the mouse can result in severe physical strain. This physical strain develops because, for the hand, even the smallest of postural shifts can increase or decrease stresses on the hand and fingers. Previously, mice were designed without sufficient consideration for the best postures of the fingers, wrist and forearm. The reported number of mouse over-use related injuries are increasing and in some industries the injury rates rival and even surpass those of keyboard related injuries. These injuries are collectively referred to as repetitive stress injuries (RSI).
The areas of the body most vulnerable to repetitive stress injuries are the soft tissues of the fingers, wrists and shoulders. More specifically, the index finger and it's knuckle joint, the tendons responsible for extending and flexing the two button fingers (index and middle) and the muscles of the shoulder which abduct, support and are responsible for extension and flexion of the arm during mouse usage. Excessive wrist extension, particularly when associated with radial and ulnar deviation, is also linked to long term tendon and nerve damage. Additionally, current mouse design provides no position for the user to rest the hand without removing the hand from the mouse and the concomitant return of the hand to the mouse. This constant activation of the shoulder muscle and joint is extremely harmful and can lead to long term damage.
Index finger abduction in normal mice results from the combination of several factors. The need to grip the mouse with the ring and little fingers in opposition to the thumb, effectively tethers the ring finger to the side of the mouse. Consequently the movement of the index finger is greatly restricted and forced into a state of continual abduction as a consequence of the linkage to the ring finger. This configuration also forces the thumb and ring and little fingers into constant contraction. Additionally, by necessity, the ring finger is placed on the side of the mouse and can't be moved to what would be a natural position because of the possibility of actuating the right button. This position, causes a myriad of problems including:
a) Restriction of the movement of the index finger to the left button, which necessitates pronation of the entire forearm to accomplish. PA1 b) Restriction of the movement by the fingers and a limitation on the range of fine control. This necessitates a shift of movement activation from the fingers to the wrist and shoulder. PA1 c) The right button position on conventional mice doesn't allow alternative grip positions with the ring finger thereby exacerbating the strain imposed on all fingers. PA1 d) Excessive pronation of the forearm while using conventional mice is almost unavoidable. The low position of left button combined with tethering the ring finger to the right side of the mouse forces excess pronation. Usually, the left button slopes away to the left exacerbating the problems. PA1 e) By providing only one position for thumb placement with no alternative, pronation is necessarily enforced. PA1 1. providing better, less stressful, finger placement; PA1 2. allowing hand release by providing the ring finger with alternative resting and grasping surfaces while avoiding activation of the right button; PA1 3. allowance for decreased pronation of the wrist and hand; PA1 4. allow greater range of finger movement by releasing the ring finger from the tethered position encountered when using conventional mice; PA1 5. improved design for hand and finger relaxation, control and movement; and PA1 6. allow natural curvature of fingers, thereby reducing or eliminating finger extension stresses.
The width of the mouse and the placement of the left button exacerbates the problem further by placing stress on the ring finger's joint and its tendons. To worsen the situation, the index and middle fingers are either in constant extension in readiness to actuate the button or levering at the joint to depress the button, thereby forcing the muscles of the two fingers into a state of either constant contraction or constant repetitive motion. This causes stress of the tendons and muscles in the forearm.
There have been several attempts to solve these problems. Mice have been designed with palm knobs and enlarged square ends. These designs, however, aggravate the above identified problems. The thumb and ring finger are brought into constant contraction and require the continual extension of the index and middle fingers over the activating buttons causing stress of the tendons in the forearm. As with other mouse designs, the ring finger is necessarily placed on the side of the mouse, leading to the myriad of problems outlined above.
Additionally, pronation of the hand is increased. By elevating the palm, the left stretch of the forefinger is increased and more reach is required thereby necessitating increased pronation. While these designs may provide some hand support, there is no finger extensor relief and they restrict fine finger control.
Alternatively, mice have been designed which support the entire hand, but don't provide the normal detrimental grip. These designs have a variety of shortcomings as well. They take away fine finger control thereby requiring all fine movement to occur at the wrist or shoulder. These pushing, pulling and lateral side-to-side movements are generated at the wrist or shoulder. Continual use of such devices could lead to injuries to these two vulnerable areas. These mice also are difficult or impossible to use in an intermittent fashion due to the necessity of gripping, positioning, removing and returning the operator's hand, and may lead to decreased productivity in some applications.
Lastly, some mice have been designed to have specific hand shaped ergonomics. While these mice provide comfortable positions in which to rest the hand, it is difficult to use these mice in the usual intermittent fashion with just the fingers. The pivot point, or anchor, for mouse designs such as these is no longer the wrist as found in conventional mice, therefore fine control is reduced. This design also shifts much of the fine control initiation to the shoulder, again creating the possibility of long term damage to the shoulder. Such specific hand shaped mice also will not accommodate a variety of hand sizes, necessitating the production and marketing of an excessively large variety of sizes in both left and right hand configurations. These designs generally lack proper surfaces for mouse movement using just the fingers.